HVAC low voltage wiring (zoning) question

[aunsafe2015]

Two questions about the attached wiring diagram:

1) Do the two black circles identified by the red arrows (towards top of diagram) simply represent wire nuts/connectors? So each nut would have 3 wires coming out of it: 1 going to thermostat; 1 going to air handler; and 1 going to zone panel?

2) For the 24v transformer (see green lines & blue arrows/box), I was assuming something like this would work: https://www.amazon.com/dp/B001DVQ5KO/?tag=atomicindus08-20. But then I saw the "NOTE" in the blue box.

Can somebody explain that "NOTE" to me in simpler terms?

Is it saying that, rather than connecting both the R and B/common from the transformer to the zoning panel, as depicted by my green lines, you would instead connect the R from the transformer to the zoning panel, and the B/common from the transformer to the indoor unit (air handler)? So that means you would have 1 wire from the transformer to the zoning panel and 1 wire from the transformer to the indoor unit? And the "B" terminal on the zoning panel would simply be empty?

Or is it saying that the B/common from the transformer should be connected to BOTH the zoning panel B terminal and the B/common on the indoor unit (presumably using a wire nut)?

Both options seem strange to me so I thought I'd run it by you folks here.

Thanks for any input!

 

[jmiller_2308]

I am not a HVAC professional but after studying this stuff for several weeks to fix what the "professional" did to my system I think I can comment.

Two questions about the attached wiring diagram:

1) Do the two black circles identified by the red arrows (towards top of diagram) simply represent wire nuts/connectors? So each nut would have 3 wires coming out of it: 1 going to thermostat; 1 going to air handler; and 1 going to zone panel?

In these diagrams the black dot you are referring to indicates that the crossing wires are connected. If there were no dot they are not connected. So yes, you are correct that the 2 identified wires are connected to the thermostat, "communicating indoor unit", and the zone panel.

2) For the 24v transformer (see green lines & blue arrows/box), I was assuming something like this would work: https://www.amazon.com/dp/B001DVQ5KO/?tag=atomicindus08-20. But then I saw the "NOTE" in the blue box.

You would need to look at the total VA being driven by that transformer to know if it will work. VA is Volts times Amps of the equipment. In my limited experience, the zone dampers are likely the largest consumer while the relays and thermostats attribute almost negligible draw. You should be able to get consumption by looking on the equipment for a label that identifies amps or possibly even a VA number and you already know that the volts is 24; otherwise cross reference any part numbers you can find on the web for specifics.

Again, I have limited experience but it seems that I most often see 40va transformers used in HVAC so I'd be a bit concerned that the 20va you identified would be large enough.

Can somebody explain that "NOTE" to me in simpler terms?

Is it saying that, rather than connecting both the R and B/common from the transformer to the zoning panel, as depicted by my green lines, you would instead connect the R from the transformer to the zoning panel, and the B/common from the transformer to the indoor unit (air handler)? So that means you would have 1 wire from the transformer to the zoning panel and 1 wire from the transformer to the indoor unit? And the "B" terminal on the zoning panel would simply be empty?

Or is it saying that the B/common from the transformer should be connected to BOTH the zoning panel B terminal and the B/common on the indoor unit (presumably using a wire nut)?

Both options seem strange to me so I thought I'd run it by you folks here.

Thanks for any input!

I'd love to hear other opinions on this but I believe they are saying that you want to tie the B/common wires of all transformers together so that they are common across all transformers. You could do this with a wire nut or possibly by connecting two wires at the B/common connection on your zone panel.

 

[aunsafe2015]

I am not a HVAC professional but after studying this stuff for several weeks to fix what the "professional" did to my system I think I can comment.







In these diagrams the black dot you are referring to indicates that the crossing wires are connected. If there were no dot they are not connected. So yes, you are correct that the 2 identified wires are connected to the thermostat, "communicating indoor unit", and the zone panel.

Nice, that's what I thought. Thanks.

You would need to look at the total VA being driven by that transformer to know if it will work. VA is Volts times Amps of the equipment. In my limited experience, the zone dampers are likely the largest consumer while the relays and thermostats attribute almost negligible draw. You should be able to get consumption by looking on the equipment for a label that identifies amps or possibly even a VA number and you already know that the volts is 24; otherwise cross reference any part numbers you can find on the web for specifics.



Again, I have limited experience but it seems that I most often see 40va transformers used in HVAC so I'd be a bit concerned that the 20va you identified would be large enough.

I'm actually fine on size. There's a page of the manual I didn't include here that explains how to size. My setup would only have 3 dampers (2.5 va each) and the zoning panel, so I believe my calculation using the manual's formula had me at needing 12va minimum.

I'd love to hear other opinions on this but I believe they are saying that you want to tie the B/common wires of all transformers together so that they are common across all transformers. You could do this with a wire nut or possibly by connecting two wires at the B/common connection on your zone panel.

Thanks for sharing your thoughts. So your guess would be that if you only have a single transformer, you'd simply connect it to the zoning panel as shown by the two green lines?

Thanks again for weighing in. I'm not sure I'm going to do this project myself and I would prefer to hire somebody,, but what you said in your first sentence is exactly the reason I'm researching this. I have trouble finding a pro I really trust to do things right so I make sure I have at least a decent idea how it's supposed to be done so I can understand what the pro is doing and why (and have some idea how to fix things if the pro messes up...).

To be clear, I don't sit there and watch them while they work. I know they hate that. I just like to do my research so when they finish up I know what to look for to get a hint of whether they did it right.

 

[brewchief]

2.5 va per damper sounds low but could be depending on brand.
Transformers should be in phase as well, at least on the similar systems I've dealt with. To check the phasing simply hook it up as shown and measure voltage between the R wires on each transformer, a few volts is normal but if it's 50 ish swap the R and C wires on the aux transformer.

Sent from my SM-G965U using Tapatalk

 

[jmiller_2308]

So your guess would be that if you only have a single transformer, you'd simply connect it to the zoning panel as shown by the two green lines?

Yes, that would be my guess but if your setup is the same as your diagram I think you do have another transformer.

I believe your diagram is for a Trane ZONE950AC52ZA zone panel. If so, 9 of the installation manual says "Note: R from the Indoor Unit/Relay Panel is not connected because power is provided from a field supplied 24VAC transformer". The power being supplied is to the zone panel and all the sensors, dampers, and any additional panels but specifically not the thermostat or the communicating indoor unit.

When I originally looked at your diagram I wondered why R (24VAC) only ran from what I called the thermostat to the communicating indoor unit but after reading the note in 9 I suspect that you have a transformer in the communicating indoor unit that is supplying 24VAC to the thermostat over that R wire.

Ok, so realizing that the B wire leaving the zone panel is the B/common of the 24VAC field-supplied transformer, and assuming that the B/common going to the communicating indoor unit is also the B/common of the transformer in the communicating indoor unit, you will have completed the Note from 12 by simply connecting them with wire nuts as you originally suggested. It will be exactly the way your diagram shows it.

 

[SGKent]

one generally doesn't tie two transformers together. The secondary winding has a phase to it, and reversing it between transformers would be a bad thing. The only time two transformers are generally tied together is when it is done in some kind of electronic device where it is a permanent installation to where the folks setting it up know the phase of each transformer, or where the output of one transformer becomes the input of the next transformer, and they are in isolation. In a HVAC system the unit often contains the transformer which goes to everything. In this case the installer provides it. The two black dots represent a connection as others have said. The green highlighted wires supply 24V AC. The wattage or sometimes called VA (there is a difference technically) is the combined need of all the devices. I imagine there is a code that specifies what percentage of combined VA is the suggested size of the transformer. Meaning if the total VA is say 50 VA then one might want a 75 VA transformer rather than run it at full capacity.

 

[aunsafe2015]

Yes, that would be my guess but if your setup is the same as your diagram I think you do have another transformer.



I believe your diagram is for a Trane ZONE950AC52ZA zone panel. If so, 9 of the installation manual says "Note: R from the Indoor Unit/Relay Panel is not connected because power is provided from a field supplied 24VAC transformer". The power being supplied is to the zone panel and all the sensors, dampers, and any additional panels but specifically not the thermostat or the communicating indoor unit.



When I originally looked at your diagram I wondered why R (24VAC) only ran from what I called the thermostat to the communicating indoor unit but after reading the note in 9 I suspect that you have a transformer in the communicating indoor unit that is supplying 24VAC to the thermostat over that R wire.



Ok, so realizing that the B wire leaving the zone panel is the B/common of the 24VAC field-supplied transformer, and assuming that the B/common going to the communicating indoor unit is also the B/common of the transformer in the communicating indoor unit, you will have completed the Note from 12 by simply connecting them with wire nuts as you originally suggested. It will be exactly the way your diagram shows it.

Nice, thanks so much for the response (and taking a look at the manual!). What you say makes sense.


And thanks to everybody else for chiming in as well!

 

[fitter30]

Transformer like this can be foot or box mounted and has circuit breaker on 24v side
https://www.amazon.com/dp/B07M6N4LDD/?tag=atomicindus08-20